Paint compositions

Abstract

This invention discloses paint compositions and the preparation of paint compositions which can be spread and dried to give electrically conductive films. The paint compositions contain colloidal carbon particles. The graphite is wet ground and this is found to give a particular shape to the resulting particles and a particle size distribution such that the dried conductive films have a low resistivity in the range of about 0.1 to 10 ohms/square. Such films produce useful heat outputs when relatively low voltage currents are passed through them and so they are suitable for application to the walls of a building for use as a central heating system.

I claim: 
     
       1. An electrically conductive paint composition comprising dispersed in a hardenable binder a total of from 25 to 75 percent p.v.c. of conductive particles of which from 14 to 70 percent p.v.c. are graphite platelets which have been formed by wet grinding graphite and from 2 to 35 percent p.v.c. are colloidal size carbon particles having a particle size from 20 to 60 millimicrons as determined by electron microscopy, the weight ratio of colloidal size carbon particles to graphite platelets being from 0.1 to 0.4, the composition having a paint-like consistency and being capable of being brushed or sprayed so as to give on a surface an even film from about 0.001 to 0.005 inch thick having an electrical resistance of less than 10 ohms per square. 
     
     
       2. A paint composition as claimed in claim 1 containing colloidal size carbon particles having a particle size of from 20 to 50 millimicrons as determined by electron microscopy. 
     
     
       3. A paint composition as claimed in claim 1 in which the hardenable binder is an inorganic silicate binder. 
     
     
       4. A paint composition as claimed in claim 3 which contains as a dispersing agent a sodium naphthalene sulphonic acid/formaldehyde condensate. 
     
     
       5. A paint composition as claimed in claim 1 in which the hardenable binder is an organic ammonium silicate binder. 
     
     
       6. A paint composition as claimed in claim 1 in which the hardenable binder is an aqueous emulsion binder. 
     
     
       7. A paint composition as claimed in claim 6 which contains as a dispersing agent a nonyl phenylethylene oxide condensate. 
     
     
       8. A paint composition as claimed in claim 1 in which the hardenable binder is an organic solvent soluble resin binder. 
     
     
       9. A paint composition as claimed in claim 8 which contains as a dispersing agent Ros aniline base. 
     
     
       10. A hardened electrically conductive paint film formed from a paint composition as claimed in claim 1. 
     
     
       11. The paint composition of claim 1 wherein the ratio of carbon particles to graphite platelets is about 0.4. 
     
     
       12. The paint composition of claim 1 wherein the ratio of carbon particles to graphite platelets is about 0.2 to 0.3. 
     
     
       13. The paint composition of claim 1 wherein p.v.c. of conductive particles is from 45 to 75 percent.